The sintering of ores, ore fines and other materials has been conventionally carried out on travelling grate type units where the ore and a fuel and flux material are placed on a travelling grate machine. The material is ignited at its surface and air drawn downwardly through the ignited mixture and, upon the flame front reaching the bottom of the bed of material, the hot sinter is discharged from the grate. The hot sinter is then generally cooled in a separate cooling unit. Although in some instances air may be drawn through the material on the grate, such usage usually greatly increases the size of suction fans used for a given rate of sinter production. The sintering operation has been plagued with problems of dust and other pollution because of the nature of the sintered material, and generally expensive dust collecting and recycling apparatus is necessary if pollution is to be controlled.
It has been found that by providing a plurality of cooling zones and by directing heated dust-laden air from a first cooling zone to the sintering zone of the travelling grate apparatus, the dust from the sintered material will be filtered from the air by the material being sintered and air from a further cooling zone can be exhausted directly to the atmosphere with strand cooling efficiently and cleanly effected. Strand cooling, i.e., cooling of the sintered material while the material is still on the travelling grate apparatus, without need for the transfer of highly-heated material and the resultant dust and other transfer problems associated therewith, is highly advantageous. It has now been discovered that dust removal in a cooling step is enhanced by the use of a purging zone in which higher pressure air agitates the dust in the sintered material to further remove dust therefrom.